Frequency Specific Stimulation Sequences

ABSTRACT

A signal processing arrangement generates electrical stimulation signals to electrode contacts in an implanted cochlear implant array. An input sound signal is analyzed to determine characteristic frequency components. One or more stimulation events are requested based on the timing and amplitude of the frequency component. A frequency-specific stimulation sequence (FSSS) is generated for stimulation of a plurality of adjacent electrode contacts. The FSSS starts with a stimulation pulse to the highest-frequency, most-basal electrode contact of the adjacent electrode contacts, ends with a stimulation pulse to the lowest-frequency, most-apical electrode contact of the adjacent electrode contacts, and reaches a maximum stimulation amplitude at a frequency-specific location within the cochlea corresponding to a natural traveling wave maximum. The electrode stimulation signals are then generated from the FSSS for delivery by the electrode contacts to adjacent auditory neural tissue.

This application claims priority from German Patent Application DE102015104614, filed Mar. 26, 2015, from U.S. Provisional PatentApplication 62/212,642, filed Sep. 1, 2015, and from U.S. ProvisionalPatent Application 62/212,643, filed Sep. 1, 2015, all of which areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to hearing implant systems, and morespecifically, to techniques for producing electrical stimulation signalsin such systems.

BACKGROUND ART

A normal ear transmits sounds as shown in FIG. 1 through the outer ear101 to the tympanic membrane 102, which moves the bones of the middleear 103 (malleus, incus, and stapes) that vibrate the oval window andround window openings of the cochlea 104. The cochlea 104 is a longnarrow duct wound spirally about its axis for approximately two and ahalf turns. It includes an upper channel known as the scala vestibuliand a lower channel known as the scala tympani, which are connected bythe cochlear duct. The cochlea 104 forms an upright spiraling cone witha center called the modiolar where the spiral ganglion cells of theacoustic nerve 113 reside. In response to received sounds transmitted bythe middle ear 103, the fluid-filled cochlea 104 functions as atransducer to generate electric pulses which are transmitted to thecochlear nerve 113, and ultimately to the brain.

Hearing is impaired when there are problems in the ability to transduceexternal sounds into meaningful action potentials along the neuralsubstrate of the cochlea 104. To improve impaired hearing, hearingprostheses have been developed. For example, when the impairment isrelated to operation of the middle ear 103, a conventional hearing aidmay be used to provide mechanical stimulation to the auditory system inthe form of amplified sound. Or when the impairment is associated withthe cochlea 104, a cochlear implant with an implanted stimulationelectrode can electrically stimulate auditory nerve tissue with smallcurrents delivered by multiple electrode contacts distributed along theelectrode.

FIG. 1 also shows some components of a typical cochlear implant system,including an external microphone that provides an audio signal input toan external signal processor 111 where various signal processing schemescan be implemented. The processed signal is then converted into adigital data format, such as a sequence of data frames, for transmissioninto the implant 108. Besides receiving the processed audio information,the implant 108 also performs additional signal processing such as errorcorrection, pulse formation, etc., and produces a stimulation pattern(based on the extracted audio information) that is sent through anelectrode lead 109 to an implanted electrode array 110.

Typically, the electrode array 110 includes multiple electrode contacts112 on its surface that provide selective stimulation of the cochlea104. Depending on context, the electrode contacts 112 are also referredto as electrode channels. In cochlear implants today, a relatively smallnumber of electrode channels are each associated with relatively broadfrequency bands, with each electrode contact 112 addressing a group ofneurons with an electric stimulation pulse having a charge that isderived from the instantaneous amplitude of the signal envelope withinthat frequency band.

In some coding strategies, stimulation pulses are applied at a constantrate across all electrode channels, whereas in other coding strategies,stimulation pulses are applied at a channel-specific rate. Variousspecific signal processing schemes can be implemented to produce theelectrical stimulation signals. Signal processing approaches that arewell-known in the field of cochlear implants include continuousinterleaved sampling (CIS), channel specific sampling sequences (CSSS)(as described in U.S. Pat. No. 6,348,070, incorporated herein byreference), spectral peak (SPEAK), and compressed analog (CA)processing.

FIG. 2 shows the major functional blocks in a typical cochlear implantsignal processing system wherein band pass signals are processed andcoding to generate electrode stimulation signals to stimulationelectrodes in an implanted cochlear implant electrode array. Forexample, commercially available Digital Signal Processors (DSP) can beused to perform speech processing according to a 12-channel CISapproach. The initial acoustic audio signal input is produced by one ormore sensing microphones, which may be omnidirectional and/ordirectional. Preprocessor Filter Bank 201 pre-processes the initialacoustic audio signal with a bank of multiple band pass filters, each ofwhich is associated with a specific band of audio frequencies—forexample, a digital filter bank having 12 digital Butterworth band passfilters of 6th order, Infinite Impulse Response (IIR) type—so that theacoustic audio signal is filtered into some M band pass signals, B₁ toB_(M) where each signal corresponds to the band of frequencies for oneof the band pass filters. Each output of the CIS band pass filters canroughly be regarded as a sinusoid at the center frequency of the bandpass filter which is modulated by the envelope signal. This is due tothe quality factor (Q≈3) of the filters. In case of a voiced speechsegment, this envelope is approximately periodic, and the repetitionrate is equal to the pitch frequency. Alternatively and withoutlimitation, the Preprocessor Filter Bank 201 may be implemented based onuse of a fast Fourier transform (FFT) or a short-time Fourier transform(STFT). Based on the tonotopic organization of the cochlea, eachelectrode contact in the scala tympani often is associated with aspecific band pass filter of the external filter bank.

FIG. 3 shows an example of a short time period of an audio speech signalfrom a microphone, and FIG. 4 shows an acoustic microphone signaldecomposed by band-pass filtering by a bank of filters into a set ofsignals. An example of pseudocode for an infinite impulse response (IIR)filter bank based on a direct form II transposed structure is given byFontaine et al., Brian Hears: Online Auditory Processing UsingVectorization Over Channels, Frontiers in Neuroinformatics, 2011;incorporated herein by reference in its entirety:

for j = 0 to number of channels − 1 do  for s = 0 to number of samples −1 do   Y_(j)(s) = B_(0j) * X_(j) (s) + Z_(0j)   for i = 0 to order − 3do    Z_(ij) = B_(i+1,j) * X_(j)(s) + Z_(i+1,j) − A_(i+1,j) * Y_(j)(s)  end for   Z_(order − 2,j) = B_(order − 1,j) * X_(j)(s) −A_(order − 1,j) * Y_(j)(s)  end for end for

The band pass signals B₁ to B_(M) (which can also be thought of asfrequency channels) are input to a Signal Processor 202 which extractssignal specific stimulation information—e.g., envelope information,phase information, timing of requested stimulation events, etc.—into aset of N stimulation channel signals S₁ to S_(N) that representelectrode specific requested stimulation events. For example, channelspecific sampling sequences (CSSS) may be used as described in U.S. Pat.No. 6,594,525, which is incorporated herein by reference in itsentirety. For example, the envelope extraction may be performed using 12rectifiers and 12 digital Butterworth low pass filters of 2nd order,IIR-type.

A Pulse Generator 205 includes a Pulse Mapping Module 203 that applies anon-linear mapping function (typically logarithmic) to the amplitude ofeach band-pass envelope. This mapping function—for example, usinginstantaneous nonlinear compression of the envelope signal (maplaw)—typically is adapted to the needs of the individual cochlearimplant user during fitting of the implant in order to achieve naturalloudness growth. This may be in the specific form of functions that areapplied to each requested stimulation event signal S₁ to S_(N) thatreflect patient-specific perceptual characteristics to produce a set ofelectrode stimulation signals A₁ to A_(M) that provide an optimalelectric representation of the acoustic signal. A logarithmic functionwith a form-factor C typically may be applied as a loudness mappingfunction, which typically is identical across all the band pass analysischannels. In different systems, different specific loudness mappingfunctions other than a logarithmic function may be used, with just oneidentical function is applied to all channels or one individual functionfor each channel to produce the electrode stimulation signals A₁ toA_(M) outputs from the Pulse Mapping Module 203.

The Pulse Generator 205 also includes a Pulse Shaper 204 that developsthe set of electrode stimulation signals A₁ to A_(M) into a set ofoutput electrode pulses E₁ to E_(M) for the electrode contacts in theimplanted electrode array which stimulate the adjacent nerve tissue. Theelectrode stimulation signals A₁ to A_(M) may be symmetrical biphasiccurrent pulses with amplitudes that are directly obtained from thecompressed envelope signals.

In the specific case of a CIS system, the stimulation pulses are appliedin a strictly non-overlapping sequence. Thus, as a typical CIS-feature,only one electrode channel is active at a time and the overallstimulation rate is comparatively high. For example, assuming an overallstimulation rate of 18 kpps and a 12 channel filter bank, thestimulation rate per channel is 1.5 kpps. Such a stimulation rate perchannel usually is sufficient for adequate temporal representation ofthe envelope signal. The maximum overall stimulation rate is limited bythe minimum phase duration per pulse. The phase duration cannot bearbitrarily short because, the shorter the pulses, the higher thecurrent amplitudes have to be to elicit action potentials in neurons,and current amplitudes are limited for various practical reasons. For anoverall stimulation rate of 18 kpps, the phase duration is 27 μs, whichis near the lower limit.

In the CIS strategy, the signal processor only uses the band pass signalenvelopes for further processing, i.e., they contain the entirestimulation information. For each electrode channel, the signal envelopeis represented as a sequence of biphasic pulses at a constant repetitionrate. A characteristic feature of CIS is that the stimulation rate isequal for all electrode channels and there is no relation to the centerfrequencies of the individual channels. It is intended that the pulserepetition rate is not a temporal cue for the patient (i.e., it shouldbe sufficiently high so that the patient does not perceive tones with afrequency equal to the pulse repetition rate). The pulse repetition rateis usually chosen at greater than twice the bandwidth of the envelopesignals (based on the Nyquist theorem).

Another cochlear implant stimulation strategy that does transmit finetime structure information is the Fine Structure Processing (FSP)strategy by Med-El. Zero crossings of the band pass filtered timesignals are tracked, and at each negative to positive zero crossing, aChannel Specific Sampling Sequence (CSSS) is started. Typically CSSSsequences are only applied on the first one or two most apical electrodechannels, covering the frequency range up to 200 or 330 Hz. The FSParrangement is described further in Hochmair I, Nopp P, Jolly C, SchmidtM, Schöβer H, Garnham C, Anderson I, MED-EL Cochlear Implants: State ofthe Art and a Glimpse into the Future, Trends in Amplification, vol. 10,201-219, 2006, which is incorporated herein by reference.

Many cochlear implant coding strategies use what is referred to as anN-of-M approach where only some number n electrode channels with thegreatest amplitude are stimulated in a given sampling time frame. If,for a given time frame, the amplitude of a specific electrode channelremains higher than the amplitudes of other channels, then that channelwill be selected for the whole time frame. Subsequently, the number ofelectrode channels that are available for coding information is reducedby one, which results in a clustering of stimulation pulses. Thus, fewerelectrode channels are available for coding important temporal andspectral properties of the sound signal such as speech onset.

One method to reduce the spectral clustering of stimulation per timeframe is the MP3000™ coding strategy by Cochlear Ltd, which uses aspectral masking model on the electrode channels. Another method thatinherently enhances coding of speech onsets is the ClearVoice™ codingstrategy used by Advanced Bionics Corp, which selects electrode channelshaving a high signal to noise ratio. U.S. Patent Publication2005/0203589 (which is incorporated herein by reference in its entirety)describes how to organize electrode channels into two or more groups pertime frame. The decision which electrode channels to select is based onthe amplitude of the signal envelopes.

In addition to the specific processing and coding approaches discussedabove, different specific pulse stimulation modes are possible todeliver the stimulation pulses with specific electrodes—i.e. mono-polar,bi-polar, tri-polar, multi-polar, and phased-array stimulation. Andthere also are different stimulation pulse shapes—i.e. biphasic,symmetric triphasic, asymmetric triphasic pulses, or asymmetric pulseshapes. These various pulse stimulation modes and pulse shapes eachprovide different benefits; for example, higher tonotopic selectivity,smaller electrical thresholds, higher electric dynamic range, lessunwanted side-effects such as facial nerve stimulation, etc. But somestimulation arrangements are quite power consuming, especially whenneighboring electrodes are used as current sinks. Up to 10 dB morecharge might be required than with simple mono-polar stimulationconcepts (if the power-consuming pulse shapes or stimulation modes areused continuously).

It is well-known in the field that electric stimulation at differentlocations within the cochlea produce different frequency percepts. Theunderlying mechanism in normal acoustic hearing is referred to as thetonotopic principle. In cochlear implant users, the tonotopicorganization of the cochlea has been extensively investigated; forexample, see Vermeire et al., Neural tonotopy in cochlear implants: Anevaluation in unilateral cochlear implant patients with unilateraldeafness and tinnitus, Hear Res, 245(1-2), 2008 Sep. 12 p. 98-106; andSchatzer et al., Electric-acoustic pitch comparisons insingle-sided-deaf cochlear implant users: Frequency-place functions andrate pitch, Hear Res, 309, 2014 March, p. 26-35 (both of which areincorporated herein by reference in their entireties).

In a normal hearing ear, one frequency component consecutivelystimulates multiple neural populations. This phenomenon was described asthe “travelling wave” as shown in FIG. 5 from Von Békésy, Georg.Experiments in hearing. Ed. Ernest Glen Wever. Vol. 8. New York:McGraw-Hill, 1960 (incorporated herein by reference in its entirety).That is, in response to a pure tone, the basilar membrane resonates in atravelling wave (the ascending numbers within FIG. 5) which graduallygrows in amplitude (the dashed lines in FIG. 5) as it moves along thecochlear duct from the stapes (base) toward the helicotrema (apex).

One quality of the travelling wave that is partly reflected in moderncochlear implant systems is that each frequency component reaches a peakamplitude at a specific spot within the cochlea (the tonotopic principlediscussed above). These spectro-temporal properties can also be observedin the activity of cat's cochlear nerve fibres shown in FIG. 6 fromSecker Walker et al, Time domain analysis of auditory nerve fiber firingrates, J Acoust Soc Am, 88(3), 1990, p. 1427-1436 (incorporated hereinby reference in its entirety). FIG. 6 shows neural activity in thecochlear nerve over time at nerve fibres with different characteristicfrequencies in response to synthetic vowels. One dominant frequencycomponent in the synthetic vowel stimuli is the fundamental frequency(F0), which in FIG. 6 can be clearly identified as a regular patternstarting at high frequencies and ending several milliseconds later atlow frequencies. The black curve in the shaded box in FIG. 6 indicatesthe frequency-specific time delays or the neural responses. Higherfrequency components also can be observed between the F0 structures; forexample, harmonics that are visible between 1800 and 1000 Hz. Similar tothe F0 structures, they start at high frequency fibers and end somemilliseconds later at low frequency fibers. This spectro-temporalexcitation behaviour is not currently explicitly implemented in cochlearimplant systems.

Loeb G., Are cochlear implant patients suffering from perceptualdissonance? Ear Hear, 26, 2005, p. 435-450 (incorporated herein byreference in its entirety) describes that phase-locking occurs over asubstantial length of the cochlea. Furthermore, the action potentialsexhibit a coherent spatial gradient with the steepest and most rapidlychanging gradient of the phase occurring next to the place of theresonant frequency. At this point, the travelling wave starts tosignificantly slow down and dissipates. The phase gradient is believedto substantially contribute to pitch perception, especially in loudsituations where harmonics are not resolved.

Existing coding approaches take into account some of the temporalproperties of the acoustic signal. CIS determines frequency-specificenvelopes which inherently contain a certain amount of information aboutindividual low frequency components such as the fundamental frequency.More advanced approaches for calculating band specific envelopes alsohave been described; for example, U.S. Patent Publication 2006/0235486(which is incorporated herein by reference in its entirety). The latterand CIS both sample the band pass envelopes with fixed rate stimulationpulses to resemble rudimentary properties of the basilar membranemovement. Other advanced systems as described in U.S. Patent Publication2011/0230934 (which is incorporated herein by reference in its entirety)explicitly extract temporal characteristics of a band pass signal byidentifying phase characteristics such as zero crossings. The describedsystem triggers channel-specific sequences of stimulation pulses at eachdetected zero crossing. Each of the foregoing arrangements attributescertain frequency components to certain stimulation places. U.S. PatentPublication 2011/0230934 also explicitly takes into account the timingof certain frequency components.

Vocoder-based cochlear implant stimulation arrangements such as CIS andN-of-M do not take into account the travelling wave properties of normalacoustic hearing. The acoustic signal is analysed by filter banks or FFTand assigned either to single intracochlear electrodes, or tosimultaneous stimulation of multiple adjacent electrodes. While filterbanks can mimic the latencies of single frequency components at theplace of stimulation, they are not able to mimic other aspects of thetravelling wave behaviour such as the spectro-temporal distribution ofthis component to neighbouring stimulation sites, starting at a morebasal site with low amplitude and ending at a more apical stimulationsite with a maximum of stimulation at a site in between. An FFT, alsoused for mimicking the tonotopic principle in a cochlear implant is nobetter able to replicate the general latency differences between thefrequency components (at the place of stimulation) nor does it providethe spectro-temporal behaviour described above.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to a signal processingarrangement and corresponding method that generates electrodestimulation signals to electrode contacts in an implanted cochlearimplant array. An input sound signal is analyzed to determinecharacteristic frequency components. For each frequency component, oneor more stimulation events are requested based on the timing andamplitude of the frequency component. For each requested stimulationevent, a frequency-specific stimulation sequence (FSSS) is generated forstimulation of adjacent electrode contacts. The FSSS starts with astimulation pulse to the highest-frequency, most-basal electrode contactof the adjacent electrode contacts, ends with a stimulation pulse to thelowest-frequency, most-apical electrode contact of the adjacentelectrode contacts, and reaches a maximum stimulation amplitude at afrequency-specific location within the cochlea corresponding to anatural traveling wave maximum. The electrode stimulation signals arethen generated from the FSSS for delivery by the electrode contacts toadjacent auditory neural tissue.

In further specific embodiments, each stimulation pulse within the FSSSactivates either a single electrode contact, or a plurality of adjacentelectrode contacts simultaneously and in-phase. Simultaneous stimulationpulses may be amplitude corrected based on Channel InteractionCompensation (CIC). The FSSS may be shorter in time for higher frequencycomponents and longer in time for lower frequency components. The FSSSmay be at least partially simultaneous on two or more electrodecontacts. For each electrode contact, the FSSS may be a Channel SpecificSampling Sequence (CSSS). The timing of each frequency component mayreflect a phase characteristic and/or frequency-specific latencycharacteristic of the frequency component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section view of a human ear with a typical cochlearimplant system designed to deliver electrical stimulation to the innerear.

FIG. 2 shows various functional blocks in a continuous interleavedsampling (CIS) processing system.

FIG. 3 shows an example of a short time period of an audio speech signalfrom a microphone.

FIG. 4 shows an acoustic microphone signal decomposed by band-passfiltering by a bank of filters into a set of band pass signals.

FIG. 5 shows the concept of the travelling wave within the cochlea.

FIG. 6 shows an example neurogram of auditory nerve fibers of a cat overtime.

FIG. 7 shows various logical steps in developing electrode stimulationsignals according to an embodiment of the present invention.

FIG. 8 shows various waveforms related to producing frequency-specificstimulation sequences for a low frequency component according to anembodiment of the present invention.

FIG. 9 shows various waveforms related to producing frequency-specificstimulation sequences for a high frequency component according to anembodiment of the present invention.

FIG. 10 shows different shapes of frequency-specific stimulationsequences.

FIG. 11 shows different amplitude and phase delay shapes offrequency-specific stimulation sequences.

FIG. 12 shows an example of steered multi-polar travelling wavestimulation.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention add to a cochlear implant system anemulation of a normal auditory physiological process which is importantfor frequency perception in normal hearing individuals, the travellingwave response of the cochlea. The added spectro-temporal featuresreflect the rise and sharp fall of excitation along the cochlea from thetravelling wave, as well as its slowing down. Embodiments of theinvention use arrangements that detect a number of relevant (i.e.spectrally spread or psychophysically unmasked) frequency components andtranslates them into stimulation sequences which can besuper-positioned. This approach can be configured for the specificnumber of individual information channels of a given patient by skippingfrequency components while transmitting distinguishable components in ahighly natural way.

FIG. 7 is a flow chart showing various logical steps in producingelectrode stimulation signals to electrode contacts in an implantedcochlear implant array according to an embodiment of the presentinvention. A pseudo code example of such a method can be set forth as:

Input Frequency and Component Level Estimation:   FilterAnalyze(input_sound, frequency_components) Frequency Specific StimulationSequences:   Code (frequency_components, stim_events)   FSSS(stim_events, fsss_seqs) Stimulation Pulse Generation:   Generate(fsss_seqs, output_pulses)The details of such an arrangement are set forth in the followingdiscussion.

As in the arrangement discussed above with respect to FIG. 2, apreprocessor signal filter bank 201 can be configured to decompose aninput sound signal into band pass frequency component signals B₁ toB_(M), step 701, representing an estimate of instantaneous inputfrequency/timing and component level/amplitude such that each band passfrequency component signal B₁ to B_(M) changes over time incharacteristic timing and amplitude. The timing of the band passfrequency component signals B₁ to B_(M) typically may reflectfrequency-specific response latencies and/or phase characteristics. Thesignal processing module 202 then processes the band pass frequencycomponent signals B₁ to B_(M) to code each frequency component, step702, as a sequence of requested stimulation events based on thefrequency component timing and amplitude.

For each requested stimulation event, a frequency-specific stimulationsequence (FSSS) output S₁ to S_(N) is generated, step 703, for at leastpartially simultaneous stimulation of adjacent electrode contacts. FIG.8 shows various waveforms related to the signal processing module 202producing an FSSS according to an embodiment of the present inventionfor a low frequency component. The top panel A in FIG. 8 shows a lowfrequency component where the circles (zero crossings) indicate specificstimulation events. Each stimulation event triggers an FSSS. The middlePanel B in FIG. 8 shows the timing of the desired neural response to theinput frequency in terms of location along the cochlea over time. Thethin horizontal lines in Panel B indicate examples of electrode-specificlocations/frequencies. The lower Panel C in FIG. 8 shows FSSSstimulation sequences on two adjacent electrode contacts that applyweighted partially simultaneous stimulation in the specific form ofChannel Specific Sampling Sequences (CSSS as described in U.S. Pat. No.6,594,525; incorporated herein by reference in its entirety).Specifically, Panel C shows that the FSSS starts with the left-moststimulation pulse to the highest-frequency, most-basal electrode contact(n+1), ends with the right-most stimulation pulse to thelowest-frequency, most-apical electrode contact (n). The FSSS is definedso as to reach a maximum stimulation amplitude at a frequency-specificlocation within the cochlea that corresponds to a natural traveling wavemaximum. Each given stimulation pulse within the FSSS activates either asingle electrode contact, or multiple adjacent electrode contactssimultaneously and in-phase.

For the low frequency component shown in FIG. 8, there is a relativelylarge phase delay and longer duration FSSS. The FSSS is typicallyshorter in time for higher frequency components and longer in time forlower frequency components. Thus, FIG. 9 shows various waveforms relatedto producing frequency-specific stimulation sequences for a highfrequency component where the phase delay is smaller and the FSSS isshorter in duration. And FIG. 10 shows different potential shapes offrequency-specific stimulation sequences.

The pulse generator 205 is configured to convert the requestedstimulation events S₁ to S_(N) to produce a corresponding sequence ofunweighted stimulation signals A₁ to A_(M) that provide an optimalelectric representation of the acoustic signal, and then apply a linearmapping function (typically logarithmic) and pulse shaping to produceweighted output pulse sequences electrode stimulation signals E₁ toE_(M) for delivery by the electrode contacts to adjacent auditory neuraltissue, step 704. Simultaneous stimulation pulses may be amplitudecorrected based on Channel Interaction Compensation (CIC). The weightedoutput pulse sequences electrode stimulation signals E₁ to E_(M) alsoare adapted to the needs of the individual implant user based on apost-surgical fitting process that determines patient-specificperceptual characteristics.

The length of the FSSS can vary based on the number of electrodechannels and the number of the CSSS per channel. The lengths of theelectrode channel CSSS per FSSS may be constant, however, varying CSSSlengths per FSSS also may be possible, such as longer CSSS at moreapical channels or longer/shorter CSSS at the maximum level of the FSSS,etc. Some embodiments also may apply a Channel Interaction Compensation(CIC) algorithm (e.g., U.S. Pat. No. 7,917,224; incorporated herein byreference in its entirety) to the amplitudes of simultaneous FSSS toprovide a desired loudness level to the user. The onset of the CSSSwithin a FSSS is controlled by the phase of the travelling wave.Subthreshold stimulation on individual electrode channels may be appliedwithin a single FSSS in order to support and maintain spontaneous actionpotentials at the stimulation locations.

Frequency specific characteristics of the FSSS such as amplitude shape,spread over electrode positions, and duration (of entire FSSS andchannel specific CSSS per FSSS) can be stored as templates in systemmemory that is accessible to the signal processing module 202. FIG. 11shows some specific examples of different amplitude and phase delayshapes of frequency-specific stimulation sequences, with a low frequencycomponent shown on the left, and a high frequency component shown on theright. The vertical lines in FIG. 11 represent time instances at whichsimultaneous stimulation is elicited. And an FSSS can be calculated forany desired frequency component by using interpolation.

Temporal overlap of an FSSS can be handled by applying simultaneousstimulation of all necessary electrodes, i.e. superposition. Spectraloverlap of two simultaneously requested interleaving FSSS can also beomitted.

The FSSS can be optimized in duration, number of stimulations, andamplitude shape to produce a the most tone-like percept in response toan acoustic presentation of a pure tone. The amplitude shape and timingof the FSSS can reproduce the envelope of the traveling wave byrepresenting portions of the traveling wave at consecutive positionsalong the cochlea (FIG. 11) starting at the base of the cochlea with lowamplitude and rising with a shallow slope up to the maximum frequencyand then falling with a steep slope towards the apex of the cochlea.Alternatively, in simplest form, the amplitude shape of the FSSS canconsist of a single stimulation event, occurring simultaneously on twoor more adjacent electrode channels. The various FSSS may overlap intime so that they can be applied in a superimposed manner. The timing ofthe stimulation event reflects the phase delay of the encoded frequencycomponent as shown in FIGS. 8 and 9. The amplitude weightings of thesimultaneous stimulation events on the adjacent electrodes reflect thefrequency specific place of the component along the cochlea. And, insome specific embodiments, the stimulation events may be selected asdescribed in U.S. Patent Publication 2009/0125082, which is incorporatedherein by reference in its entirety.

Stimulation positions which are intermediate to physical electrodepositions can be produced by weighted simultaneous stimulation of one ormore adjacent electrodes. Alternatively, a FSSS can also be compiledfrom a series of focused stimulation modes, e.g. tri- or multipolarstimulation such as phased array stimulation as shown in Bonham et al.,Current focusing and steering: modeling, physiology, and psychophysics,Hear Res, 242(1-2), August 2008, pp. 141-153; incorporated herein byreference in its entirety. The focus, amplitude and timing of thestimulation will follow the tempo-spectral shape of the traveling waveenvelope. FIG. 12 shows an example of steered multi-polar traveling wavestimulation where the focus of stimulation (circles) follows thetemporal course of the traveling wave.

Embodiments of the invention may be implemented in part in anyconventional computer programming language. For example, preferredembodiments may be implemented in a procedural programming language(e.g., “C”) or an object oriented programming language (e.g., “C++”,Python). Alternative embodiments of the invention may be implemented aspre-programmed hardware elements, other related components, or as acombination of hardware and software components.

Embodiments can be implemented in part as a computer program product foruse with a computer system. Such implementation may include a series ofcomputer instructions fixed either on a tangible medium, such as acomputer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk)or transmittable to a computer system, via a modem or other interfacedevice, such as a communications adapter connected to a network over amedium. The medium may be either a tangible medium (e.g., optical oranalog communications lines) or a medium implemented with wirelesstechniques (e.g., microwave, infrared or other transmission techniques).The series of computer instructions embodies all or part of thefunctionality previously described herein with respect to the system.Those skilled in the art should appreciate that such computerinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Furthermore, suchinstructions may be stored in any memory device, such as semiconductor,magnetic, optical or other memory devices, and may be transmitted usingany communications technology, such as optical, infrared, microwave, orother transmission technologies. It is expected that such a computerprogram product may be distributed as a removable medium withaccompanying printed or electronic documentation (e.g., shrink wrappedsoftware), preloaded with a computer system (e.g., on system ROM orfixed disk), or distributed from a server or electronic bulletin boardover the network (e.g., the Internet or World Wide Web). Of course, someembodiments of the invention may be implemented as a combination of bothsoftware (e.g., a computer program product) and hardware. Still otherembodiments of the invention are implemented as entirely hardware, orentirely software (e.g., a computer program product).

Although various exemplary embodiments of the invention have beendisclosed, it should be apparent to those skilled in the art thatvarious changes and modifications can be made which will achieve some ofthe advantages of the invention without departing from the true scope ofthe invention.

What is claimed is:
 1. A method for generating electrode stimulationsignals to electrode contacts in an implanted cochlear implant electrodearray, the method comprising: analyzing an input sound signal todetermine a plurality of characteristic frequency components, eachfrequency component having a characteristic timing and amplitude; foreach frequency component, requesting one or more stimulation eventsbased on the timing and amplitude of the frequency component; for eachrequested stimulation event, generating a frequency-specific stimulationsequence (FSSS) for stimulation of a plurality of adjacent electrodecontacts, wherein the FSSS: i. starts with a stimulation pulse to thehighest-frequency, most-basal electrode contact of the adjacentelectrode contacts, ii. ends with a stimulation pulse to thelowest-frequency, most-apical electrode contact of the adjacentelectrode contacts, and iii. reaches a maximum stimulation amplitude ata frequency-specific location within the cochlea corresponding to anatural traveling wave maximum; and generating the electrode stimulationsignals from the FSSS for delivery by the electrode contacts to adjacentauditory neural tissue.
 2. The method according to claim 1, wherein eachstimulation pulse within the FSSS activates either a single electrodecontact, or a plurality of adjacent electrode contacts simultaneouslyand in-phase.
 3. The method according to claim 2, wherein simultaneousstimulation pulses are amplitude corrected based on Channel InteractionCompensation (CIC).
 4. The method according to claim 1, wherein the FSSSis shorter in time for higher frequency components and longer in timefor lower frequency components.
 5. The method according to claim 1,wherein for each electrode contact, the FSSS is a Channel SpecificSampling Sequence (CSSS).
 6. The method according to claim 1, whereinthe timing of each frequency component reflects a phase characteristicof the frequency component.
 7. The method according to claim 1, whereinthe timing of each frequency component reflects a frequency-specificlatency characteristic of the frequency component.
 8. The methodaccording to claim 1, wherein the FSSS is at least partiallysimultaneous on two or more electrode contacts.
 9. A system forgenerating electrode stimulation signals to electrode contacts in animplanted cochlear implant electrode array, the arrangement comprising:a signal filter bank configured to analyze an input sound signal todetermine a plurality of characteristic frequency components, eachfrequency component having a characteristic timing and amplitude; asignal processing module configured to: i. request one or morestimulation events for each frequency component based on the timing andamplitude of the frequency component, and ii. generate afrequency-specific stimulation sequence (FSSS) for each requestedstimulation event for at least partially simultaneous stimulation of aplurality of adjacent electrode contacts, wherein the FSSS: a) startswith a stimulation pulse to the highest-frequency, most-basal electrodecontact of the adjacent electrode contacts, b) ends with a stimulationpulse to the lowest-frequency, most-apical electrode contact of theadjacent electrode contacts, and c) reaches a maximum stimulationamplitude at a frequency-specific location within the cochleacorresponding to a natural traveling wave maximum; and a pulse generatorconfigured to generating the electrode stimulation signals from the FSSSfor delivery by the electrode contacts to adjacent auditory neuraltissue.
 10. The system according to claim 9, wherein the signalprocessing module is configured so that each stimulation pulse withinthe FSSS activates either a single electrode contact, or a plurality ofadjacent electrode contacts simultaneously and in-phase.
 11. The systemaccording to claim 10, wherein the signal processing module isconfigured so that simultaneous stimulation pulses are amplitudecorrected based on Channel Interaction Compensation (CIC).
 12. Thesystem according to claim 9, wherein the signal processing module isconfigured so that the FSSS is shorter in time for higher frequencycomponents and longer in time for lower frequency components.
 13. Thesystem according to claim 9, wherein the signal processing module isconfigured so that for each electrode contact, the FSSS is a ChannelSpecific Sampling Sequence (CSSS).
 14. The system according to claim 9,wherein the signal processing module is configured so that the timing ofeach frequency component reflects a phase characteristic of thefrequency component.
 15. The system according to claim 9, wherein thesignal processing module is configured so that the timing of eachfrequency component reflects a frequency-specific latency characteristicof the frequency component.
 16. The system according to claim 9, whereinthe signal processing module is configured so that the FSSS is at leastpartially simultaneous on two or more electrode contacts.
 17. Anon-transitory tangible computer-readable medium having instructionsthereon for generating electrode stimulation signals to electrodecontacts in an implanted cochlear implant electrode array, theinstructions comprising: analyzing an input sound signal to determine aplurality of characteristic frequency components, each frequencycomponent having a characteristic timing and amplitude; for eachfrequency component, requesting one or more stimulation events based onthe timing and amplitude of the frequency component; for each requestedstimulation event, generating a frequency-specific stimulation sequence(FSSS) for at least partially simultaneous stimulation of a plurality ofadjacent electrode contacts, wherein the FSSS: starts with a stimulationpulse to the highest-frequency, most-basal electrode contact of theadjacent electrode contacts, ends with a stimulation pulse to thelowest-frequency, most-apical electrode contact of the adjacentelectrode contacts, and reaches a maximum stimulation amplitude at afrequency-specific location within the cochlea corresponding to anatural traveling wave maximum; and generating the electrode stimulationsignals from the FSSS for delivery by the electrode contacts to adjacentauditory neural tissue.